To save the FBX files, you need to install the AutodeskFBX package. Add the LowPolyColorChanger component to any valid object (with a mesh and an atlas texture material) and an alert box will be shown. Hit the "Install FBX Extensions" button.
This will automatically add the AutodeskFBX package and add the "HAS_AUTODESK_FBX" scripting define symbol to your project
Hit the iinstall FBX exention button
Scripting Define Symbols on Players Settings panel